Load application unit



Aug. 4, 1953 Filed Oct. 15, 1951 J. W. GAINES LOAD APPLICATION UNIT 2Sheets-Sheet l INVENTOR.

JAMES W. GAINES ATTORNEY Aug. 4, 1953 J. w. GAINES 2,647,400

LOAD APPLICATION UNIT Filed oct. 5, 1951 2 Sheets-Sheet 2 IN V EN TOR.

JAMES W. GAI NES BY [mm ATTORNEY Patented Aug. 4, 1953 UNITE-D PATENTOFFICE LOAD APPLICATION UNIT James W. Los Angeles, -Galif., assignor :to

orth American Aviation, Inc.

Application October 15, 1951, .SerialNu. 251,405

12Claims. (01. 73-88) 1 This invention applies to a load applicationunit and more particularly to a unit adapted to apply loads to curved'orstraight test panels. Present day arrangements for'applying loads totest a specimen normally involve that are glued to the specimen. Eachunit is separate and is hacked up by a rigid metal plate. These: unitsare normally attached to a test specimen by placing a vacuum *blanketover the uni-ts so that the units may be "held against the specimen bythe force of a vacuum until the glue has set. The rigid metal platesmust he shaped as nearly as possible to the contour of the test specimenwhich is a time consuming operation, and it is nearly impossible to formthe plates to the exact contour required. As a result, there is atendency to deform the test specimen when the plates are attached bymeans of the vacuum blanket. In addition, it takes a good deal of timeto attach the plates as well as to form them and it is very di-ilicultto remove the glue when the tests are completed. Solvents for the gluewill injure a windshield canopy test specimen, and scraping of the gluewill also result in damage to the specimen due to scratching.Arrangements utilizing vacuum cups as the load application units havebeen proposed, but these have proved unsatisfactory because they aredifiicult to seal around the edges and will not produce a uniform vacuumload throughout the entire area where the unit is attached. As a resultthese load units are poorly attached to the test specimen and will notwithstand high loads. Further, these will tend to distort the "testspecimen due to the non-uniform vacuum produced.

Accordingly, it is an object of this invention to provide a loadapplication unit that may be easily and securely applied to a testspecimen and maybe quickly removed.

' Another object of this invention is to provide a load application unitthatdoesnotrequi-regluing to the test specimen. 7

A further object of this invention is to -pro 'vide a load applicationunit that does not require the use of substances injurious to the testspecimen.

.An additional object of this invention is to provide a load applicationunit that will withstand heavy loads and will not cause distortion.ofthe test specimen.

stillanother-object of this invention is topro wide a dead applicationunit having a plurality of .load assuming members. .Theseandiotherohiects of this invention will become apparent fromtheiollovl-mg detailed sieill) 2 scription taken in connection with theaccounpanying drawings in which Fig. 1 is a perspective sectionalview-"of the "load application uni-t applied to a test specimen,

Fig. 2 is a fragmentary inverted perspective view illustrating analternative construction of the non-porous sheet.

Fig. 3 is a plan view illustrating the use of second sheet of non-porousmaterial,

Fig. sis aview along line 4-4 ot-Fig. 3,

Fig. 5 is an elevation of a modification of the load application unit,

Fig. .6 is a plan view of portions of the bottom of a unit of the typeshown in Fig. 5, l

"Fig. "7 is a sectional view of a unit of the type of Fig. 5 associatedwith porous sheets,

Fig. 8 is a sectional view of a pad and-sheet formed from a single pieceof material,

Fig. 9 is a sectional view of a pad and sheet formed from a single pieceof material wherein the bottom portion is provided with grooves, and

"10 is a one-piece-unit of the type of Fig. associated with poroussheets.

Referring to the drawings, in a preferred em- "bodiment of thisinvention, load application unit I is made of a sheet of non-porousflexible matori-a1"? to one side of which is applied a thicker pad 3which is also of a flexible material such as sponge rubber. The pad maybe attached to the sheet "by bonding, gluing or other satisfactorymethods and should be positioned in the central portion of the sheet sothat the periphery 4 of the sheet extends beyond the pad on all sides.on the other side of the pad a plurality of fiat, rigid plates '5 areattached by gluing or other suitable methods. Theseplates should bespaced from each other as illustrated in order to allow 'flexure of theunit. It is normally desirable to put a ll-shaped groove 6 in the padbetween the plates to facilitate flexure of the unit. Attached byscrewthreads. welding or other suitable means to each plate 5 is afitting 1 adapted to receive .a ,load producing member such as wirecable 8. The unit may be constructed as large or as small .as desiredand as many plates 5 may be attached to the pad as necessitated ,by thesize of the unit -;and the number of load producing membersfa ,toheattached. Means arealso provided for pro- .ducing avacuum-beneathsheet 2 which may be accomplished by .nroyiding a length of tubing asprojecting .ithrough one of the plates. the red and the sheet. Thistubing opens to {the bottom oisheet I and .is aria-medic receive avacuum hose it on its other end. The vacuum. hose is plate member 5 mayreceive a load producing member if desired. Detachment of the unit fromthe test specimen is accomplished by merely releasing the vacuum beneathsheet 2which allows easy removal of the unit from the test specimen. Asa vacuum is produced beneath sheet 2 the I It is normally preferred tointerposea vacuum sealing material l2 beneath the projecting periphery 4of sheet 2 in order to assure a'complete vacuum beneath the sheet. Thismaterial may be zinc chromate, ordinary caulking compound or othersuitable material. When the unit is removed frcm the testspecimen thissealing material will require no scraping and can be easily washed offwith a solvent that will not injure a transparentwindshield canopy.

It; is also generally desirable to provide a sheet of porous material l3between sheet 2 and test specimen ll. Sheet l3 should be of lesser widthand length dimensions than sheet 2approximately the dimensions of pad3-and positioned in the center so that the periphery ll of sheet 2projects beyond porous sheet 13 in all directions. This porous sheet maybe of any suitable material such as'wire-screenor a loosely woven fabricsuch as burlap. The function of porous sheet I3 is toprevent sheet 2from'sealing itself off at. a location other than the periphery of thissheet, thus assuring that there is a uniform vacuum throughout the areabeneath pad3. V

Another method of assuring that the vacuum is uniform beneath sheet l.is to provide the bottom surface of the unit with grooves 14 or otherirregularities in the area beneath the pad, portion in the mannerillustrated in Fig. 2 in which the load application unit is invertedfrom the position shown in Fig. 1. Withthis modification it isunnecessary t use a porous sheet l3 because the grooves will' permitcomplete exhaustion of the air from beneath the sheet and preventsealing at positions other than the periphery of sheet 2.

In certain instances it may be desirable to provide a second sheet ofnon-porous material l5 as illustrated in Figs. 3 and 4.; This sheetshould be of a highly flexible material and may be a thin sheet of aplastic material such as a vinyl derivative. Sheet Iii-should haveanaperture H5 in its central portion'dimensioned so as to admit pad 3while allowing" the periphery of the aperture to engagethe periphery ofsheet 2. Additional sealing material-'12 should be provided 4 betweensheet 15 and periphery 4 of sheet 2, and a ring of the sealing materialmay be provided between sheet 15 and test specimen H well beyond theperiphery of sheet 2. The use of this additional non-porous sheetassures a complete vacuum beneath the load application unit and willassist in rescaling around the periphery of the unit should the seal bebroken.

A 'modificationof this invention is-illustrated in Fig. 5-in which thebottom surface of sheet I is provided with depending tabs [1. When aunit provided with these tabs is associated with a testspecimen, tabs[1, sheet 2, and the test specimen cooperate to provide a plurality ofseparate chambers I8; A suitable vacuum aperture such as tubing 9 isprovided to each of these chambers.

.When the unit is applied, vacuum sealing compound l2 may be disposedbeneath each of the tabs to. assure that the chambers are separatelysealed from each other. To assure a complete and; uniform vacuum beneathsheet 2, each chamber l8 may beprovided with a sheet of porous materiali3, as illustrated in Fig. '7, or the surface of sheet 2 may be providedwith grooves M or other indentations as shown in Fig.6 or of the typeillustrated in Fig. 2. v

When such a modified test unit is applied to a test specimen a separatevacuum line 10 may be attached to each of chambers 18 or these vacuumlines maybe manifolded. together by manifold 20, as shown in- Fig. 5, ifdesired. The vacuum lines and manifold are connected with suitablevacuum pumps l9. Thus, for example, if failure of the test specimen isanticipated at a certain area a separate vacuum line may be applied tothe chambers in that area while the other chambers may be manifoldedtogether. Thus failure of the test specimen at the critical area willnot effect adherence of the unitin other positions.

It is possible as a further modification to construct sheet 2 and pad 3out of a single piece of material in any of the above describedembodiments. Fig. 8 illustrates a pad and sheet of the type of Fig. 1formed from one piece of material 2|. In Fig. 9 is shown a one-piece padand sheet unit 21 having grooves to assure complete exhaustion of airfrom beneath the unit in the manner in the embodiment of Fig. 2. A testunit having a plurality of chambers 18 yet made from a single piece ofmaterial is illustrated in Fig. 10.

It should be clearly understood that the above detailed description isto be taken by way of illustration only and not to be taken by way oflimitation, the spirit and scope of this invention being limited onlybythe terms ofthe appended claims. a

I claim:

l. A load application. unit comprising a sheet of flexible materiahoneside of which is adapted to engage a test specimen andassume the contourthereof; a pad of flexiblematerial attached to the opposite side of saidsheet; a plurality of laterally spaced reinforcing members secured tosaid pad-remote from said sheet, each of said reinforcing members beingprovided with means adapted'to engage load producing means; and meansfor exhausting-the air from beneath said sheet thereby securing saidunit to said specimen.

2. A device as recited in claim 1;.in which the periphery of said sheetof flexible material projects beyond said. pad-on all sides thereof,-and

includes in addition a secondsheet of flexible riphery and saidspecimen.

3.. A device as recited in claim 1 which includes in addition a sheet ofporous material adapted to be interposed between said sheet of flexiblematerial and said specimen with the periphery of said sheet of flexiblematerial projecting beyond the periphery of said sheet of porousmaterial.

4. A device as recited in claim 1 in which the surface of said sheetadapted to engage said test specimen is provided with groove means forfacilitating the exhaustion of air from beneath said unit.

5. A load application unit comprising a sheet of non-porous flexiblematerial one side of which is adapted to engage a test specimen andassume the contour thereof; a pad of flexible material attached to theopposite side of said sheet; a plurality of rigid plate members securedto said pad remote from said sheet; said plates being disposed in spacedrelationship with each other for permitting flexure of said pad and saidsheet; each plate being provided with means adapted to engage loadproducing means; said pad and said sheet having apertures therethroughfor allowing exhaustion of air from beneath said sheet for holding saidunit to said specimen.

6. A load application unit comprising a sheet of non-porous flexiblerubber, the underside of which is adapted to complementarily engage atest specimen; a pad of flexible rubber attached to the opposite side ofsaid sheet; a plurality of rigid metal plates attached to the surface ofsaid pad remote from said sheet; said plates being disposed in spacedrelationship with each other, said pad being provided with groovesbetween said plates for facilitating fiexure on said unit, said unitbeing provided with an aperture communicating with the underside of saidsheet; and means connected with said aperture for creating a vacuumbetween said sheet and said specimen or attaching said unit thereto.

7. A load application unit for a test specimen comprising a sheet ofporous material engaging the surface of said specimen; a sheet ofnonporous material adapted to overlie said porous sheet with itsperiphery extending beyond said sheet onto the surface of said specimen;a vacuum sealing substance disposed beneath the periphery of saidnon-porous sheet; a pad of flexible material having substantially thewidth and length dimensions of said porous sheet attached to the centralportion of said non-porous sheet on the side remote from said poroussheet; a plurality of rigid plate members attached to said pad remotefrom said non-porous sheet, said plate members being disposed in spacedrelationship and adapted to engage load producing means; a second sheetof non-porous material adapted to overlie the periphery of said firstmentioned non-porous sheet; and means for producing a vacuum betweensaid first mentioned non-porous sheet and said specimen thereby securingsaid unit thereto.

8. A load application unit comprising an elongated flexible member, oneside of which is adapted to engage a test specimen; a plurality of rigidplate members disposed in laterally spaced relationship and attached tosaid flexible member remote from said side adapted to engage a testspecimen; and means for exhausting the air from beneath said flexiblemember for securing said unit to a test specimen.

9. A device as recited in claim 8 in which said side adapted to engage atest specimen is provided with a plurality of depending tab portionsadapted to cooperate with said test specimen to provide a plurality ofchambers therewith, and including means for evacuating each of saidchambers.

10. A load application unit comprising a sheet of flexible material, oneside of which is provided with a plurality of depending tab portions andadapted to engage the surface of a test specimen thereby cooperatingwith said specimen to provide a plurality of chambers between said sheetand said specimen; a pad of flexible material attached to the oppositeside of said sheet; a plurality of rigid plates attached to said padremote from said sheet in a spaced relationship with each other, saidplates being provided with means adapted to engage load producing means;and means for evacuating each of said chambers for holding said unit tosaid specimen.

11. A device as recited in claim 10 in which said sheet of flexiblematerial is provided with groove means between said tab portion forfacilitating the exhaustion of air from said chambers.

12. A device as recited in claim 10 including in addition a sheet ofporous material for each of said chambers and adapted to be receivedtherein.

JAMES W. GAINES.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,151,584 Bugatti Mar. 21, 1939 2,319,675 Grinter May 18, 19432,413,737 Weaver Jan. 7, 1947

